Rotary switch with spring loaded cam means

ABSTRACT

A single-pole single-throw, single-pole double-throw, doublepole single-throw or double-pole double-throw switch used primarily with a variable resistor, in which not only accurate operations are secured but also the lowering of a dielectric strength, due to an arc or abrasive dust or soot, is prevented in cutting off a circuit which develops an especially high surge current.

United States Patent [1 1 Tanaka et al.

[ ROTARY SWITCH WITH SPRING LOADED CAM MEANS [75] Inventors: Heiroku Tanaka; Katsuyoshi Onda,

both of Osaka, Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan 22 Filed: Aug. 6, 1973 21 Appl. No.: 385,677

Related U.S. Application Data [63] Continuation of Ser. No. 195,438, Nov. 3, 1971,

abandoned.

[52] U.S. Cl. 200/153 L, 200/67 C, 338/198 [51] Int. Cl. H01h 3/42 [58] Field of Search... 200/6, 67 C, 153 L, 153 LA, 200/153 N, 153 LB, 155 R; 174/137 R, 137 A;338/172, 198

[56] References Cited UNITED STATES PATENTS 2,320,837 6/1943 Turney 338/198 3O 33 28 23 22 ll Sept. 3, 1974 2,721,243 [0/1955 Daily 200/67 C 3,510,613 5/1970 Borden 200/67 C 3,748,627 7/1973 Zdanys, Jr. 338/198 Primary Examiner-Robert K. Schaefer Assistant Examiner-Gerald P. Tolin Attorney, Agent, or FirmStevens, Davis, Miller & Mosher [57] ABSTRACT 12 Claims, 12 Drawing Figures I'vlx I PAIENIEB SEP 3 I974 SHEET 1 0F 3 FIG.4

ROTARY SWITCH WITH SPRING LOADED CAM MEANS This is a continuation, of U.S. Pat. application Ser. No. 195,438, filed Nov. 3, I971.

The present invention relates to a single pole singlethrow, single-pole double-throw, double pole singlethrow or double-pole double-throw switch used primarily with a variable resistor.

An object of the present invention is to provide a switch wherein not only accurate operations are secured but also the reduction in dielectric strength is prevented which otherwise might occur due to an arc or abrasive dust or soot generated therelby when cutting off a circuit developing an especially high surge current.

Another object of the present invention is to provide a switch comprising a switch housing, fixed contactors mounted on the housing, a pivot mounted on the housing, a movable contactor rotatably mounted on the pivot for making and breaking the fixed contactor, a switching plate of insulating material with a protrusion on the under side thereof for engaging with an engaging aperture or between a couple of mating protrusions formed on the movable contactor, a di-casting cam mounted on the switching plate and provided with a positioning protrusion on the under side thereof for engaging with an engaging aperture formed in the housing, a switching spring interposed between the cam and switching plate in such a manner as to separate them from each other and a switch cover of metal fixed on the housing which has a positioning aperture formed on the bottom thereof which engages with a positioning protrusion formed on the upper side of the cam, wherein a switching protrusion formed on the upper side of the cam for performing change-over operations is projected through a guide aperture formed in the bottom of the switch cover, the housing being provided with a groove so as to separate the fixed contactors from other conductors, and an upright wall or recession being provided along the entire periphery of the housmg.

According to the present invention, the groove formed on the housing in such a manner as to separate the fixed contactors from other line parts prevents the lowering of the dielectric strength which otherwise might occur between the live parts due to abrasive dust or soot generated at the time of making and breaking the switch. Also, the upright wall or recess provided along the entire periphery of the housing prevents the lowering of the dielectric strength between the live parts and the switch cover (for grounding) made of metal. As a result, even when using the switch with a circuit in which a high surge current flows, it is possible to prevent the lowering of the dielectric strength which otherwise would .occur due to an arc or abrasive dust or soot developed by such an are at the time of making and breaking the switch. Further, the present invention provides a very useful switch with simple construction and low cost.

Still another object of the present invention is to provide a switch comprising a rectangular housing of insulating material, fixed contactors located on a first diagonal line of the rectangular housing, pivots disposed on a second diagonal line of the housing in such a manner as to cross with the first diagonal line, a movable contactor rotatably mounted on each of the pivots for making and breaking each of the fixed contactors, a drive plate of insulating material disposed on the movable contactor and the pivots for driving the movable contactor, a switching plate of insulating material disposed on the drive plate which has a protrusion on the under side thereof which in turn engages with an engaging aperture formed at the center of a line connecting the engaging protrusions formed on the drive plate, a dicasting cam mounted on the switching plate and having a positioning protrusion on the under side thereof which engages with an engaging aperture formed in the housing, a switching spring acting to separate the cam from the switching plate, and a switch cover of metal mounted on the housing which has at its bottom an engaging aperture for engagement with a positioning protrusion formed on the upper side of the cam, wherein an engaging protrusion provided at a point on a diagonal line of the under side of the driving plate engages between a couple of protrusions or with an aperture formed on the movable contactor, and a switching protrusion provided on the upper side of the cam is projected through a guide aperture formed in the bottom of the switch cover.

According to the present invention, a fixed contactor is provided at a point on the first diagonal line of the housing while a pivot carrying a rotatable movable contactor which mates with the fixed contactor is located at a point on the second diagonal line of the housing. Also, the driving plate for driving the movable contactor is provided with a protrusion on the under side thereof for engagement between a couple of protrusions or an aperture formed in the movable contactor. Further, the switch according to the invention is so constructed that the drive plate is driven around a supporting point on the line connecting the protrusions. This arrangement makes possible accurate switching operations and no incomplete contact will occur even in the case of great wear of one of the contactors.

The above and other objects, features and advantages will be made apparent by the detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view of an embodiment of the present invention mounted with a variable resistor;

FIG. 2 is an enlarged sectional side view of the embodiment;

FIG. 3 shows a front view of the switch whose cover is removed;

FIG. 4 shows a front view of a housing constituting part of the switch;

FIG. 5 is a perspective view showing a switch plate and a cam secured with each other by means of a switching spring;

FIG. 6 is a front view of a switch cover coupled with a resistor cover;

FIG. 7 is a side view of another embodiment of the present invention mounted with a variable resistor;

FIG. 8 is an enlarged front view of a switch housing provided with the contactors;

FIG. 9 is an enlarged sectional side view along the line IX IX of FIG. 8; 4

FIG. 10 shows an exploded perspective view of parts of the switch;

FIG. 11 shows a front view of the switch whose cover is removed; and

FIG. 12 is a front view showing a switch cover coupled with a resistor cover. 7

. ment 5 and a resistor cover 6. The cover 6 contains a contactor carrier 7 having a contactor (not shown) which slides on the resistance element 5 with the rotation of the operating shaft 2. Numeral 8 shows a switch according to the present invention mounted on the back of the resistor cover 6 in such a manner as to turn on and off with the rotation of the operating shaft 2.

The construction of the switch 8 will be now described in detail. Numeral 9 shows a rectangular housing of non-flammable insulating material which is integrated with an upright wall 10 along the entire periphery thereof. This upright wall is provided for the purpose of preventing the lowering of a dielectric strength between live parts, which will be described later, and the switch metal cover. A terrace-like portion 36 is formed on the inner surface of the housing 9 and a through hole 37 is formed at the terrace-like portion 36. The surface of the terrace-like portion is substantially flat and parallel with the surface of the remaining bottom portion 38 of the housing. A pivot post is mounted on the housing 9 piercing through the through hole 37 at the terrace-like portion. A pair of fixed contactors 11 and 12 secured with outer terminals are located on the bottom portion of housing 9. Numeral 13 shows a movable contactor with one of its ends disposed between the fixed contactors 11 and 12 and the other end rotatably supported on the terrace-like portion 36 of the housing 9 by the pivot post 15 so that the free end disposed between the fixed contactors l1 and 12 is spaced apart from the surface of the bottom portion 38 of the housing 9. The pivot post 15 is electrically connected with an outer terminal 14. The movable contactor 13 is brought into contact with and detached from the fixed contactors 1 1 and 12 with its rotation. Numeral 16 shows an engaging aperture formed in the movable contactor 13, and numeral 17 a groove formed on the housing 9 in such a manner as to separate the fixed contactors 11 and 12 from the pivot 15 in order to prevent a reduction of the dielectric strength which otherwise might occur due to abrasive dust or soot developed at the time of making and breaking of the switch. Numeral 18 shows a protrusion integrated with the upright wall 10 and projected inward therefrom. This protrusion is provided with an engaging aperture 19.

Numeral 20 shows a switching plate of insulating material which has on its under side an integrated rod-like protrusion 2 l for engaging with the aperture 16 formed in the movable contactor 13. At an end of the switching plate above the aperture 19, there is provided a hole 22. Numeral 23 shows a di-casting cam provided with a positioning protrusion 24 on the under side thereof,

which engages, through the hole 22 of the switching plate 20, with the engaging hole 19 formed in the protrusion 18 of the housing 9. The positioning protrusion 25 provided on the upper side of the cam along the same axis as the protrusion 24 engages with the positioning apertures 27 and 28 formed in the top wall of the switch cover 26 and the bottom of the resistor cover 6 attached to the top wall of the switch cover 26 respectively. The cam 23 is thus rotatable around the positioning protrusions 24 and 25 as a supporting point. On the upper side of the cam'23, there are a couple of switching protrusions 29 and 30 apart from each other,

which are projected into fan-shaped guid apertures 31 and 32 formed in the switch cover 26 and resistor cover 6 respectively. The switch cover 26 is of a box-shaped one with its underside open and holds the housing 9 by means of a plurality of bent legs 33 provided on its open underside. The switching operating section 34 on the contactor carrier 7 mounted on the operating shaft 2 is fitted in between the switching protrusions 29 and 30 of the cam 23. Numeral 35 shows a switching spring suspended between the engaging portion 36 formed on the switching plate 20 and an aperture of the cam 23 in such a manner as to separate them from each other.

Explanation will be made now of the operation of the switch with the above-described construction. When the operating shaft 2 is rotated, the contactor carrier 7 mounted on it is also rotated. Since the operating portion 34 mounted on the contactor carrier 7 is fitted in between the switching protrusions 29 and 30 of the cam 23, the rotation of the operating shaft 2 causes the cam 23 to rotate with the positioning protrusions 24 and 25 as a supporting point. As a result, the switching plate 20 moves in a direction opposite to that of the rotation of the cam 23 because of the switching spring 35 suspended between the cam 23 and the switching plate 20. The rod-like protrusion 21 formed on the under side of the switching plate 20 engages with the aperture 16 formed in the movable contactor 13, which is moved by the switching plate 20 in the .same direction. Since the switching spring 35 functions to separate the cam 23 and the switching plate 20 from each other, the switching plate 20 causes the rod-like protrusion 21 to keep the movable contactor 13 in contact with either the fixed contactor 11 or 12. With the rotation of the operating shaft 2, the cam 23 rotates and then the switching plate 20 moves, with the result that the movable contactor 13 is brought into contact with the fixed contactors 11 and 12 alternately. In other words, the switch operates as a single-pole double-throw one.

Referring to the operation of the variable resistor, the contactor mounted on the contactor carrier 7 slides on the resistance element 5 on the base plate 4 when the operating shaft 2 is rotated, making it possible to take out a desired resistance from between the middle terminal electrically connected with the contactor and one of the outer terminals connected with the ends of the resistance element 5.- y g Although the above-described embodiment includes only a single-pole double-throw switch, itis obvious that the invention can be also applied to a single-pole single-throw switch. Also, the" upright wall 10 on the periphery of the housing 9 may be replacedby a recess along the entire periphery thereof. Further, instead of the rod-like protrusion 21 of the switching plate 20 with the aperture 16 in the movablecontactor 13, the

rod-like protrusion 21 of the switching plate 20 may be engaged with a couple of protrusions which may be formed on both sides of the movable contactor 13.

As another embodiment of the present invention, a double-pole single-throwswitch which is interlocked with a variable resistor will be now explained with reference to FIGS. 7 to 12. In FIG. 7, the reference numeral 101 shows a variable resistor section, numeral 102 shows a rotational operating shaft, numeral 103 a bearing through which the operating shaft 102 passes and which is mounted on the base plate 104, on which not only the resistance element 105 but the metal resistor cover 106 are attached. The cover 106 contains a contactor carrier 137 (shown in FIG. 9) carrying the contactor (not shown) which slides on the resistance element 105 with the rotation of the operating shaft 102. Numeral 107 shows a switch section according to an improvement of the invention which is mounted on the back of the resistor cover 106 in such a manner as to be turned on and off with the rotation of the operating shaft 102.

The construction of the switch section 107 will be now described in detail with reference to FIGS. 8 to 1 1. The reference numeral 108 shows a rectangular housing of non-flammable insulating material which has an upright wall 109 along the entire periphery thereof which is integral with the housing. This upright wall 109 is provided for the purpose of preventing the reduction of the dielectric strength between the switch metal cover and live parts which will be described later. The housing 108 carries at two points on the upper side thereof the fixed contactors 1 and 110 secured with outer terminals. Numerals 111 and 111' show movable contactors located on the housing 108 which come into contact with and are detached from the fixed contactors 110 and 110'. These movable contactors are rotatably mounted on the pivots 113 and 113' respectively which are electrically connected with outer terminals 112 and 112'. The movable contactors 111 and 111 are provided with protrusions 114 and 114 on both sides of each of their ends which is farther from the pivots 113 and 113. The fixed .contactors 110 and 110' are located in a diagonal line which is crossed with another diagonal line on which the pivots 113 and 113' are situated, and as a result the protrusions 114 and 114' of the movable contactors 111 and 111 are also located in a diagonal line. Numeral 115 shows a narrow groove formed in the housing 108 in such a manner as to separate the fixed contactors 110 and 110' from each other and the fixed contactors 110 and 110' from the pivots 113 and 113 thereby preventing the lowering of the dielectric strength which otherwise might occur due to abrasive dust or soot developed at the time of making and breaking the switch. Numeral 116 shows a protrusion integrated with the upright wall 109 of the housing 108 and projecting inwardly. This protrusion is provided with an engaging aperture 117. Numeral 118 shows a rectangular drive plate of insulating material with which a pair of engaging protrusions 119 and 119' (119 is not shown) are formed integrally at the ends of a diagonal line on the under side thereof,

At the ends of the other diagonal line, there are provided flat thicker portions 120 and 120' on the under side of the drive plate 118, while an engaging aperture 121 is formed at the center thereof. The engaging protrusion 119 and 119' of the drive plate 118 are engaged with the protrusions 114 and 114 of the movable contactor as 111 and 111 respectively with a little freedom. The thicker portions 120 and 120 are in contact with the flat tops of the pivots 113 and 113', so that the drive plate 118 is held horizontal. Numeral 122 shows a switching plate of insulating material disposed on the upper side of the drive plate, the under side of which is integrated with a rodlike protrusion 123 for engaging with the aperture 121. The end of the switching plate 122 above the engaging aperture 117 formed in the protrusion 116 of the housing 108 is provided with a hole 124. Numeral 125 shows a di-casting cam provided with a positioning protrusion 126 on the lower end thereof which engages with the engaging aperture 117 in the protrusion 116 of the housing 108 through the hole 124. The positioning protrusion 127 on the top of the cam 125 engages with the positioning apertures 129 and 130 formed in the top wall of the switch cover 128 and in the bottom of the resistor cover 106, respectively, so that the cam may be located on the same axis as the positioning protrusion 126. A couple of protrusions 131 and 131 which are formed apart from each other on the upper side of the cam 125 are projected through the fan-shaped guide apertures 132 and 133 formed in the switch cover 128 and the resistor cover 106. The switch cover 128 is a box-shaped one with its under side open and holds the housing 108 by means of a plurality of bent legs 134 provided on its open under side. The switch operating portion 138 on the contactor carrier 137 mounted on the rotational operating shaft 102 is fitted in between the switching protrusions 131 and 131' of the cam 125 projected into the resistor cover 106. Numeral 135 shows a switching spring suspended between the engaging portion 136 formed on the switching plate 122 and an aperture of the cam 125 in such a manner as to separate them from each other.

The operation of the switch with the above-described construction will be now explained. Rotating the operating shaft 102 causes rotation of the contactor carrier 137 mounted thereon. Since the operating portion 138 on the contactor carrier 137 is fitted in between the switching protrusions 131 and 131' of the cam 125, the rotation of the operating shaft 102 causes the cam 125 to rotate with the positioning protrusions 126 and 127 as a supporting point. As a result, the switching plate 122 moves in a direction opposite to the cam because of the switching spring 135 suspended between the cam 125 and the switching plate 122. The rod-like protrusion 123 on the under side of the switching plate 122 is engaged with the aperture 121 formed in the drive plate 118, and the drive plate 118 moves in the same direction as the switching plate 122. Since the cam 125 and the switching plate 122 are separated from each other by means of the switching spring 135, the drive plate 118 is rotatable around the protrusion 123 and causes the engaging protrusions 119 and 119' to keep the movable contactors 111 and 111' in contact with the fixed contactors 110 and 110 with substantially equal pressure. With the rotation of the operating shaft 102, the cam 125 rotates, and the switching plate 122 and the drive plate 118 move to bring into contact the movable contactors 111 and 111' with each other or separate them from each other, so that the switch acts as a double-pole single-throw one.

Referring now to the operation of the variable resistor, the contactor mounted on the contactor carrier 137 slides on the resistance element 105 on the base plate 104 when the operating shaft 102 is rotated, making it possible to take out a desired resistance from between the middle terminal electrically connected with the contactor and one of the outer terminals connected with the ends of the resistance element 105.

Although the above-described embodiment refers only to a double-pole single-throw switch, it is obvious that the present invention is also applicable to a double-pole double-throw switch. Also, instead of the protrusions 119 and 119' of the drive plate 118 being fitted in between the protrusions 114 and 114 formed on the movable contactors 111 and 111, the movable contactors 111 and 111 may be provided with apertures for engagement with the protrusions 119 and 119 of the drive plate 118. Further, the upright wall 109 on the entire periphery of the housing 108 may be replaced by a recess along the entire periphery thereof.

What we claim is:

1. A switch comprising:

a housing of an insulating material having a first engaging aperture and a terrace-like portion formed on the inner surface thereof, a surface of said terrace-like portion being parallel with the surface of a bottom portion of said housing;

a couple of fixed contacts mounted on said housing;

a pivot post mounted on said housing and piercing said housing through a through hole formed at said terrace-like portion;

a movable contact member, rotatably supported at one end thereof on said terrace-like portion of said housing by said pivot post, for making and breaking contact between either of said fixed contacts and said movable contact member, the other end of said movable contact member being free and spaced apart from the surface of said bottom portion of said housing, said movable contact member being provided with engaging means; switching plate of an insulating material having a protrusion formed on the under surface thereof, said protrusion being engaged with said engaging means of said movable contact member; metal cam engaged with said switching plate and having first and second positioning protrusions respectively formed on the under and upper surfaces thereof and a switching protrusion formed on the upper surface thereof, said first protrusion being engaged with said first engaging aperture;

a switching spring interposed between said cam and said switching plate so as to separate said cam and said switching plate from each other; and

a switch metal cover having a plurality of legs and both a positioning aperture and guide aperture formed in the top thereof, said switch metal cover being fixed on said housing by means of said plurality of legs, said second positioning protrusion of said cam being engaged with said positioning aperture, and said switching protrusion of said cam being projected through said guide aperture so as to perform change-operations.

2. A switch according to claim 1 wherein said engaging means includes a second engaging aperture formed in said movable contact member so as to engage with said protrusion formed on the under surface of said switching plate.

3. A switch according to claim 1 wherein said engaging means includes a couple of mating protrusions formed on said movable contact member so as to engage with said protrusion formed on the under surface of said switching plate.

' 4. A switch according to claim 1 wherein said housing is provided with grooves between said fixed contacts and also between each of said fixed contacts and said pivot post so that said grooves present the reduction of the dielectric strength between said fixed contacts and also between each of said fixed contacts and said pivot post by cutting the continuation of accumulated abrasive dust and soot therebetween.

5. A switch according to claim 4 wherein an upright wall is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivot post and fixed contacts, said upright wall preventing the reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and said pivot post by cutting the continuation of accumulated abrasive dust and soot therebetween.

6. A switch according to claim 4 wherein a recess is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivot post and fixed contacts, said recess preventing the reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and said pivot post by cutting the continuation of accumulated abrasive dust and soot therebetween.

7. A switch comprising:

a rectangular housing of an insulating material having a first engaging aperture;

a couple of fixed contacts located on one of the diagonal lines of said rectangular housing;

a couple of pivots disposed on the other diagonal line;

a couple of movable, contact members for making and breaking contact between said fixed contacts and said movable contact members, each of said movable contact members being rotatably mounted on a corresponding one of said pivots and being provided with engaging means;

a drive plate of an insulating material having a second aperture, disposed on said movable contact members, for driving said movable contact members, said drive plate having a couple of engaging protrusions formed on a diagonal line on the under surface thereof, said couple of engaging protrusions being engaged with said corresponding engaging means of said movable contact members;

a switching plate of an insulating material disposed on said drive plate and having a protrusion formed on the under surface thereof, said protrusion of said switching plate being engaged with said second aperture, said second aperture being formed in said drive plate at the center of a line connecting said couple of engaging protrusions of said drive plate;

a metal cam mounted on said switching plate and having first and second positioning protrusions respectively formed on the under and upper surfaces thereof and a switching protrusion formed on the upper surface thereof, said first positioning protrusion being engaged with said first. engaging aperprojected through said guide aperture so as to perform change-operations.

8. A switch according to claim 7 wherein said engaging means includes a fourth engaging aperture formed in each of said couple of movable contact members so as to engage with a corresponding one of said couple of engaging protrusions of said drive plate.

9. A switch according to claim 7 wherein said engaging means includes a couple of mating protrusions formed on each of said couple of movable contact members so as to engage with a corresponding one of said couple of engaging protrusions of said drive plate.

11. A switch according to claim 10 wherein an upright wall is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivots and fixed contacts, said upright wall preventing reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and each of said pivots by cutting the continuation of accumulated abrasive dust and soot therebetween.

12. A switch according to claim 10 wherein a recess is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivots and fixed contacts, said recess preventing the reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and each of said pivots by cutting the continuation of accumulated abrasive dust and soot therebetween.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3,833,783 7 Dated September 3, 1974 Inventofls). 'HEIROKU TANAKA et a1 It is certified that error appears in the above-identifiedpatent and that said Lerters Patent are hereby corrected as shown below:

At block 3l0finsert Foreign Appl icat ions Prioriry Data 7 November 5, 1970 Japan .110097 November 5, 1970 Japan .110098 November 5, 1970 Japan .110099 November 5, 1970 Japan .110100 Signed and sealed this 31st day of December 1974.

(SEAL) Attest: I

McCQY M. 15 50: JR. c. MARSHALL DANN AttestingOf-ficer Commissioner of Patents FORM PO-IOSO (10-69) v USCOMM DC oznsd eg v a u.s. GOVERNMENT PRINTING OFFICE 1909 0-366-334.

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3,833,783 Dated September 3, 1974 Invent fls). HEIRO'KU TANAKA et a1 It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

At block 3 0 "'insert Foreign Applications Priority Data November 5, 1970 Japan............ll0097 November 5, 1970 Japan.. 1100,98 November 5, 1970 Japan... ....ll0099 November 5, 1970 Japan.. ..ll0l00 Signed and sealed this 31st day of December 1974.

(SEAL) Attest: I

MCCOY M. GIBSON JR. (3. MARSHALL DANN Attesting, Officer Commissioner of Patents ORM 0459) USCOMM-DC 60376-P69 1 t l-LS, GOVERNMENT PRINTING OFFICE: 1969 0-366-334. 

1. A switch comprising: a housing of an insulating material having a first engaging aperture and a terrace-like portion formed on the inner surface thereof, a surface of said terrace-like portion being parallel with the surface of a bottom portion of said housing; a couple of fixed contacts mounted on said housing; a pivot post mounted on said housing and piercing said housing through a through hole formed at said terrace-like portion; a movable contact member, rotatably supported at one end thereof on said terrace-like portion of said housing by said pivot post, for making and breaking contact between either of said fixed contacts and said movable contact member, the other end of said movable contact member being free and spaced apart from the surface of said bottom portion of said housing, said movable contact member being provided with engaging means; a switching plate of an insulating material having a protrusion formed on the under surface thereof, said protrusion being engaged with said engaging means of said movable contact member; a metal cam engaged with said switching plate and having first and second positioning protrusions respectively formed on the under and upper surfaces thereof and a switching protrusion formed on the upper surface thereof, said first protrusion being engaged with said first engaging aperture; a switching spring interposed between said cam and said switching plate so as to separate said cam and said switching plate from each other; and a switch metal cover having a plurality of legs and both a positioning aperture and guide aperture fOrmed in the top thereof, said switch metal cover being fixed on said housing by means of said plurality of legs, said second positioning protrusion of said cam being engaged with said positioning aperture, and said switching protrusion of said cam being projected through said guide aperture so as to perform changeoperations.
 2. A switch according to claim 1 wherein said engaging means includes a second engaging aperture formed in said movable contact member so as to engage with said protrusion formed on the under surface of said switching plate.
 3. A switch according to claim 1 wherein said engaging means includes a couple of mating protrusions formed on said movable contact member so as to engage with said protrusion formed on the under surface of said switching plate.
 4. A switch according to claim 1 wherein said housing is provided with grooves between said fixed contacts and also between each of said fixed contacts and said pivot post so that said grooves present the reduction of the dielectric strength between said fixed contacts and also between each of said fixed contacts and said pivot post by cutting the continuation of accumulated abrasive dust and soot therebetween.
 5. A switch according to claim 4 wherein an upright wall is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivot post and fixed contacts, said upright wall preventing the reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and said pivot post by cutting the continuation of accumulated abrasive dust and soot therebetween.
 6. A switch according to claim 4 wherein a recess is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivot post and fixed contacts, said recess preventing the reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and said pivot post by cutting the continuation of accumulated abrasive dust and soot therebetween.
 7. A switch comprising: a rectangular housing of an insulating material having a first engaging aperture; a couple of fixed contacts located on one of the diagonal lines of said rectangular housing; a couple of pivots disposed on the other diagonal line; a couple of movable contact members for making and breaking contact between said fixed contacts and said movable contact members, each of said movable contact members being rotatably mounted on a corresponding one of said pivots and being provided with engaging means; a drive plate of an insulating material having a second aperture, disposed on said movable contact members, for driving said movable contact members, said drive plate having a couple of engaging protrusions formed on a diagonal line on the under surface thereof, said couple of engaging protrusions being engaged with said corresponding engaging means of said movable contact members; a switching plate of an insulating material disposed on said drive plate and having a protrusion formed on the under surface thereof, said protrusion of said switching plate being engaged with said second aperture, said second aperture being formed in said drive plate at the center of a line connecting said couple of engaging protrusions of said drive plate; a metal cam mounted on said switching plate and having first and second positioning protrusions respectively formed on the under and upper surfaces thereof and a switching protrusion formed on the upper surface thereof, said first positioning protrusion being engaged with said first engaging aperture formed in said housing; a switching spring acting to separate said cam from said switching plate; and a metal switch cover mounted on said housing, said switch cover having a third engaging aperture and a guide aperture formed on the top of saId metal cover, said second positioning protrusion of said cam being engaged with said third engaging aperture, said switching protrusion of said cam being projected through said guide aperture so as to perform change-operations.
 8. A switch according to claim 7 wherein said engaging means includes a fourth engaging aperture formed in each of said couple of movable contact members so as to engage with a corresponding one of said couple of engaging protrusions of said drive plate.
 9. A switch according to claim 7 wherein said engaging means includes a couple of mating protrusions formed on each of said couple of movable contact members so as to engage with a corresponding one of said couple of engaging protrusions of said drive plate.
 10. A switch according to claim 7 wherein said housing is provided with grooves between said fixed contacts and also between each of said fixed contacts and each of said pivots so that said grooves prevent the reduction of the dielectric strength between said fixed contacts and also between each of said fixed contacts and each of said pivots by cutting the continuation of accumulated abrasive dust and soot therebetween.
 11. A switch according to claim 10 wherein an upright wall is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivots and fixed contacts, said upright wall preventing reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and each of said pivots by cutting the continuation of accumulated abrasive dust and soot therebetween.
 12. A switch according to claim 10 wherein a recess is formed on said housing along the entire periphery thereof and between the side wall of said metal cover and the live portions including said pivots and fixed contacts, said recess preventing the reduction of the dielectric strength between said metal cover and each of said fixed contacts and also between said metal cover and each of said pivots by cutting the continuation of accumulated abrasive dust and soot therebetween. 